Charged for nothing

I cancelled my Telkom line on July 20. I received a bill today for line rental from August 3 - September 3, an entire month when I won't be using the line.<br> <br> When I called customer service, I was told something along the lines of line cancellation takes 30 days and that's why I'm being charged for an imaginary month of usage.<br> <br> Completely absurd.